The first U.S. postal card was issued in 1873. Prepaid postal cards were a precursor to private mailing cards and later, postcards. These four Chattanooga examples have customer credit or billing statements printed on the verso.
The first example below is from Carter-McGill Hardware Co., and is dated September 17, 1891. The second is from Trotter Bros. Wholesale Groceries and Notions, and is dated June 18, 1902.
Third example is from Tom Fritts Hardware Company, and is dated January 6, 1894. The last example is from Biese Dickinson and Blair, and is dated June 20, 1893.